Synergistic enhancement of heavy metals removal and soil nutrients for agricultural soils using novel agro-waste biomass derived washing agents

Washing with waste biomass-derived organic matter is an emerging and promising sustainable strategy for heavy metal removal and soil nutrients enhancement for agricultural soils. However, single biomass-derived agents often suffer from high material consumption and low removal efficiency, limiting their field application. To address these challenges, we optimized pineapple peel (PP), an agroforestry by-product, and developed novel compounded washing agents by integrating citric acid (CA) or ethylenediaminetetraacetic acid (EDTA) with PP (CA+PP, EDTA+PP). These agents exhibited a notable synergistic effect, significantly enhancing cadmium (Cd) and copper (Cu) removal from contaminated soils. Compared to single agents, CA+PP and EDTA+PP improved Cd and Cu removal efficiencies by up to 420.9% and 403.7%, respectively. Moreover, a facile two-stage sequential washing method combining these agents with water (CA+PP-H 2 O, EDTA+PP-H 2 O) further increased Cd and Cu removal up to 61.0% and 54.1%, respectively. This approach effectively reduced residual heavy metal concentrations below risk screening values through acid activation, complexation and cation exchange, mitigated ecological risks by decreasing exchangeable and reducible Cd fractions, alleviated soil acidification, and significantly increased soil organic carbon, nitrogen, phosphorus and potassium content. These findings highlight the potential of two-stage washing with PP-derived agents as an efficient and environmentally friendly heavy metal reduction and soil nutrients enhancement synergistic remediation strategy for agricultural soils.